In the field of image sensing technology, complementary metal oxide semiconductor (CMOS) technology is widely used. A CMOS is a circuit composed of PMOS and NMOS transistors which are complementary, and hence is called a complementary MOS, i.e., CMOS. Taking a NOT gate as an example which consists of a pair of a PMOS transistor and an NMOS transistor, the instantaneous states of the PMOS and NMOS transistors include: only the PMOS is in conduction; only the NMOS is conduction; or both of them are off. The CMOS has higher efficiency and lower power consumption than a triode circuit.
In a CMOS image sensor, the CMOS device is used to generate and output an output signal corresponding to the incident light based on an electrical signal generated by the photoelectric conversion device. The threshold voltage of the transistor used to generate the output signal may suffer a voltage drift due to the fabrication process or the like, and therefore, different output signals may be generated for the same incident light by different CMOS devices or the same CMOS devices at different times, resulting in distortion of the image obtained by the CMOS image sensor.